1. Field of the Invention
The present invention relates to mass fabrication of customized items.
2. Description of Related Art
Batch processing is a common component of mass production processes. In batch processing the number of articles that can be processed in a single batch is limited by the working area available for positioning the batch. This working area is commonly referred to as a tray. For simplicity, the term tray will be used herein to refer to any work area. The number of items that may fit on a tray is affected by the sizes and shapes of the items. In many fabrication processes, the items that make up a batch are of varying sizes and shapes. This situation arises in the manufacture of customized items, such as, for example, plastic orthodontic alignment appliances, hearing aids, protective sports gear, medical devices, glasses, orthotic shoe inserts, and the like. Examples of orthodontic alignment appliances are described in U.S. Pat. No. 5,975,893 and U.S. Patent Application Publication No. 2005/0082703, both of which are incorporated herein by reference. Both the '893 patent and the '703 publication are assigned to the assignee of the present application.
Plastic orthodontic appliances of the type disclosed in the '893 patent and the '703 publication are manufactured as sets or series of incremental position adjustment appliances. Each series of incremental position adjustment appliances is custom made for each patient. The appliances are worn by the patient in sequence to incrementally realign and/or reposition the patient's teeth.
Molds for creating the appliances are manufactured by downloading three-dimensional CAD models of the molds to a rapid prototyping (“RP”) apparatus, such as, for example, a stereolithography or photolithography machine. The manufacturing facility then creates the appliances using the molds.
The RP apparatus fabricates batches of molds. Each batch is arranged on a tray having fixed dimensions. Typically, the tray is rectangular. Computer-generated images of the molds in each batch are mapped into a computer-generated field representing the tray. In a typical RP system for fabricating orthodontic appliance molds, CAD images of the molds are stored in a memory queue. These images are then mapped onto a virtual tray having the dimensions of the actual RP apparatus on which the molds are built. In some RP systems the mapping software arranges the mold images into columns on the tray by following the same sequence in which the images are arranged in the queue. The columns are then arranged sequentially on the virtual tray. The images, which may be of varying shapes and sizes, are thus located on the virtual tray with little if any regard for the heights or widths of the images. As explained in detail below, this process results in a great deal of wasted material, and more trays must be used to fabricate a given number of molds. As the number of trays increases, so do fabrication time and cost.